Diffraction dissociation of both the beam and target particles has been observed in 150-GeV/c π−p interactions in the Fermilab 30-in.-bubble-chamber-proportional-wire-chamber hybrid spectrometer. The dissociations are observed as recoil systems opposite leading particles, the signals of which are separated from background where appropriate by a variant of the Van Hove sector cut, thus allowing the high-mass portion of the spectrum to be observed. Pion dissociation has a cross section of 1758±105 μb, divided among two-, four-, and six-prong events; some ρ0 production is seen and comes primarily from the π−→2π−π+ channel. The proton dissociation cross section is 1726±100 μb, again divided among two-, four-, and six-prong events. The final state contains a neutron more frequently than a proton in the two-and six-prong events, a proton more frequently in the four-prong events. Production of Δ++ is observed in the p→pπ+π− dissociations.Received 15 March 1979DOI:https://doi.org/10.1103/PhysRevD.21.1726©1980 American Physical Society

The production of ${K}_{S}$, $\ensuremath{\Lambda}$, $\overline{\ensuremath{\Lambda}}$, and $\ensuremath{\gamma}$ in ${\ensuremath{\pi}}^{\ensuremath{-}}p$ collisions at 147 GeV/c is analyzed. Cross sections, rapidity, Feynman-$x$, and ${{p}_{T}}^{2}$ distributions are presented and compared to charged-particle production. The energy dependence of multiplicities in ${\ensuremath{\pi}}^{\ensuremath{-}}p$ and $\mathrm{pp}$ collisions is shown. A new scaling form for the correlation of neutral- and charged-particle multiplicities is presented for compilations of $\ensuremath{\pi}p$ and $\mathrm{pp}$ data.

In this paper we present new data for the reactions π−p→pslow+X− and π−p→πfast− + X+ at 147 GeV/c. This is the first time that experimental information on these two processes has been obtained using the same apparatus at Fermilab energies. The triple-Regge formalism is applied to the differential cross sections dσ/dMx2 of both reactions using all the data at present available in the literature. A good description of the data is obtained when parameters from a triple-Regge fit of the reaction pp → p + X are used, together with the assumption of factorization of the pomeron and the reggeons. The equality of the dσ/dMx2 distributions of the two reactions may be explained in terms of an interesting assumption in the framework of the independent quark model and imposes an additional relation between the triple-Regge terms.

The experimentally determined average charged-particle multiplicities, $〈{n}_{X}〉$, of the systems, $X$, produced in the following reactions for 147 GeV/c incident pion momentum are presented as functions of the square of the invariant mass of $X$, ${{M}_{X}}^{2}$, and of $|t|:{\ensuremath{\pi}}^{\ensuremath{-}}p\ensuremath{\rightarrow}{\ensuremath{\pi}}_{\mathrm{fast}}^{\ensuremath{-}}X$, ${\ensuremath{\pi}}^{\ensuremath{-}}p\ensuremath{\rightarrow}\mathrm{pX}$, ${\ensuremath{\pi}}^{\ensuremath{-}}p\ensuremath{\rightarrow}{\ensuremath{\Delta}}^{++}X$, ${\ensuremath{\pi}}^{\ensuremath{-}}p\ensuremath{\rightarrow}{({\ensuremath{\pi}}^{\ensuremath{-}}{\ensuremath{\pi}}^{+})}_{{\ensuremath{\rho}}^{0}}X$, and ${\ensuremath{\pi}}^{\ensuremath{-}}p\ensuremath{\rightarrow}{\ensuremath{\Lambda}}^{0}X$. Details of the analysis are discussed. These data can be fit by the expression $〈{n}_{X}〉=A+B \mathrm{ln} {{M}_{X}}^{2}+C|t|$ and the coefficients obtained for $B$ are equal within their uncertainties. $C$ is significantly different from zero only for ${\ensuremath{\pi}}^{\ensuremath{-}}p\ensuremath{\rightarrow}{\ensuremath{\pi}}_{\mathrm{fast}}^{\ensuremath{-}}X$. These results and $〈{n}_{X}〉$ data from other inclusive and total-inelastic-reaction studies are discussed in terms of a simple model which assumes contributions to $〈{n}_{X}〉$ from the target-fragmentation, the central, and the beam-fragmentation regions in the case of total-inelastic reactions. For inclusive reactions, either the beam or target fragmentation is replaced by an exchange-particle-fragmentation contribution. The $s$, $t$, and ${{M}_{X}}^{2}$ dependence of the parameters of the model are deduced from triple-Regge considerations. The data are found to be consistent with the model and values are presented for the parameters.

The inclusive production of the Δ++(1232) resonance in π−p collisions at 147 GeV/c has been studied. The Δ++ is found to be produced in comparable amounts in four-, six-, eight-, and ten-prong events. The Feynman-x, t′, PT2, and the decay angular distributions of the Δ++ are found to be consistent with the predictions of a one-pion-exchange model with absorption. Essentially all of the Δ++ are found to be associated with a Δ++π− low-mass enhancement. The Δ++ cross section is approximately constant from 11 to 205 GeV/c, which could indicate that the Δ++ is a decay product of a target-fragmentation object. While the one-pion-exchange character of the Δ++ production and the target-fragmentation character of the Δ++π− low-mass enhancement can both be described in terms of a Deck-type diagram, a Monte Carlo study indicates that any mechanism that produces particles with limited transverse momentum will yield a Δ++π− low-mass enhancement.Received 30 June 1977DOI:https://doi.org/10.1103/PhysRevD.18.3099©1978 American Physical Society

A study of charged particle production in 147 GeV/c π−p collisions yields no evidence for an electrically neutral central region or corresponding rapidity plateau. The results do indicate that electric charge and transverse momentum may be locally conserved over small intervals on the rapidity axis. These results support a picture in which the observed hadrons are emitted in clusters whose quantum numbers vary as a function of rapidity and reflect the incident channel quantum numbers at the extremes of the rapidity scale.

The results of a study of the reaction π-p→π-π-π+p at 2 147 GeV/c carried out at the Fermilab Proportional Wire 30″ Bubble Chamber Hybrid Spectrometer are reported. More than 92% of the cross-section ((670±41) μb) for this reaction is contained in those for proton and pion diffraction dissociation. The cross-sections for pion diffraction events with three-pion invariant mass in given regions are in agreement with values obtained by extrapolation of fits to data at lower incidentpion momenta. ρ0π- events make an important contribution in the A1 and A2 mass regions, and the data are consistent with contributions from f0π- in the A3 mass region. The cross-section for proton diffraction events is in agreement with a smooth extrapolation of the data at lower momentum.